You and your husband have obviously discussed your differing sexual needs many times in the course of your marriage and unless there is a typo in your original post the suggestion that you could take a lover came from him.
If I am right that your husband would be agreeable to your having a lover, that it one very big hurdle cleared in advance.
Whether you would be better off with a single man as a lover, or with a married man in the same position as yourself, I cannot pretend to say.
Obviously, if your lover is single, there isn't a risk of hurting his wife, but there is a greater risk that he might either end the relationship to you when he realises that you are not going to leave your husband for him, or that his availability might actually lead to you wanting a divorce.
A married lover with a wife who either no longer wants or is able to have sex would better understand your background.
As long as she too is able to accept that her husband has a relationship to another woman you may well be able to have a meaningful relationship to each other without destroying either marriage, or needing to feel guilty.
Whether it is a good idea in your situation or not is really something only you can decide.
To my mind a relationship of this kind shouldn't be kept hidden from your husband or the other man's wife.
And no, I do not think you would be selfish to take a lover, the alternatives are either that you remain frustrated or that you divorce a husband who you are fond of.
But please do be careful and remember the risk of sexually transmitted disease.